RFR: 8264975: java/net/DatagramSocket/DatagramSocketMulticasting.java fails infrequently [v2]

[Daniel Fuchs]

> Please find below a fix that will make `java/net/DatagramSocket/DatagramSocketMulticasting.java` more resilient to the rare case where addresses bound to a network interfaces are updated while the test is running.
> 
> Instead of using `NetworkInterface::equals` to compare network interfaces, the test now use `NetworkConfiguration::isSameInterface` which only looks at the network interface name and index and ignore the addresses which are bound to it.

Daniel Fuchs has updated the pull request incrementally with one additional commit since the last revision:

  Add a comment for the non-obvious case where ni1 == null || ni2 == null

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Changes:
  - all: https://git.openjdk.java.net/jdk/pull/4313/files
  - new: https://git.openjdk.java.net/jdk/pull/4313/files/aa5dea6b..d090333b

Webrevs:
 - full: https://webrevs.openjdk.java.net/?repo=jdk&pr=4313&range=01
 - incr: https://webrevs.openjdk.java.net/?repo=jdk&pr=4313&range=00-01

  Stats: 3 lines in 1 file changed: 3 ins; 0 del; 0 mod
  Patch: https://git.openjdk.java.net/jdk/pull/4313.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/4313/head:pull/4313

PR: https://git.openjdk.java.net/jdk/pull/4313